The present invention relates to apparatus for delivering fuel to an engine, and in particular to a cheek plate unloading pump for delivering fuel to an engine.
There are various known mechanisms for delivering fuel to an internal combustion engine. Increased fuel economy and improved exhaust emissions from vehicles with internal combustion engines are goals of these known mechanisms. To achieve these goals, systems have been devised which vary the amount of fuel delivered to an engine in response to one or more engine operating conditions. Some systems utilize microprocessors which receive information about variable engine operating conditions from sensors and which produce a signal to control the rate of fuel flow to the engine according to a program stored in the microprocessor. Many different engine operating conditions may be sensed. For example, the ambient air temperature, the rate of air flow into the engine, engine water temperature or oil temperature, manifold vacuum, and engine speed all may be sensed. In addition, one or more properties of the exhaust emissions may be sensed. One such system is shown in U.S. Pat. No. 3,630,643.
In some microprocessor controlled systems, a microprocessor controls an electric motor which drives a fuel pump. For example, in the system disclosed in U.S. Pat. No. 3,935,851, a number of engine operating conditions are sensed, and a microprocessor varies the voltage of the current supplied to an electric motor which drives the fuel pump. When operating conditions dictate an increased fuel supply, the voltage to the fuel pump drive motor is increased. In the event of a failure of the electronic components, the microprocessor will fail to deliver current for the pump drive motor, and the engine receives no fuel and thus cannot operate.
In other microprocessor controlled systems, a microprocessor controls the length of time a fuel injector remains open to regulate the flow of fuel to the engine. An example of such a system is described and illustrated in U.S. Pat. No. 3,971,348. Such systems are also vulnerable to failure of the electronic components since the engine is totally inoperative if the fuel injectors do not receive a signal from the microprocessor.
Similarly, the system disclosed in U.S. Pat. No. 3,949,714 is vulnerable to electronic failure. In this system, sensors send information relating to operating parameters to a microprocessor which in response generates a control signal to actuate a solenoid. The solenoid controls pump output through a servo valve which is spring biased to a position corresponding to minimum output from the pump. Accordingly, upon failure of the electronic components, the spring bias shifts the pump to its minimum output and the engine becomes inoperable.
The system disclosed in U.S. Pat. No. 3,630,643 includes a variable displacement engine-driven fuel pump. The flow output of the pump is controlled by a microprocessor which responds to engine operating conditions. The pump is biased toward maximum flow output. Accordingly, if the microprocessor fails, the pump will deliver the maximum quantity of fuel, without regard to the engine's requirements. The most likely result is flooding of the engine.
The above mentioned microprocessor controls are effective to control the fuel supplied to an engine to maximize engine efficiency and improve emissions. However, when the microprocessor or electronic components fail, the vehicle may become totally inoperable because fuel cannot be delivered to the engine in a quantity which would enable the engine to operate. The vehicle cannot be driven to a repair facility, but instead must either be towed or the repairs must be made on location. Alternatively, the delivery of fuel to the engine may be uncontrolled and extremely inefficient.